Developing a strategy to trap As3+ within naturally occurring minerals is promising for water decontamination. Contextually, tooeleite, a mineral containing As3+ and Fe3+ in a sulfate medium, could be a suitable candidate. But, tooeleite is typically known to form at high concentrations of both Fe3+ and As3+ in strongly acidic pH (similar to 2.5) (acid mine drainage (AMD)-like conditions), which reduced its applicability to this narrow regime only. Herein, the nucleation and growth of tooeleite mineral has been probed at the molecular level, which follows the nonclassical nucleation pathway, deviating from classical nucleation theory. Importantly, contrary to the above-mentioned narrow regime, primary FeAsS clusters of an average diameter of 0.78 nm, nearly identical to tooeleite locally, have been found within a wide range of Fe/As solutions in situ, even at much lower concentrations (10 ppm of Fe concentration, Fe3+/As3+ = 1.5) and higher pH (pH similar to 6), where bulk tooeleite formation is unexpected. Furthermore, when subjected to AMD-like conditions, these extracted clusters readily convert into an extended tooeleite-like bulk crystalline phase. This observation that tooeleite-like clusters can originate and remain stable under conditions like >= 10 ppm Fe, Fe3+/As3+ = 1.5, and pH similar to 2 to 6 naturally opens up the possibility of mineralization as a permanent removal technique for As3+ from contaminated water.

The speciation of arsenic (As) in aqueous environments, particularly the relative concentration ratio of the highly toxic and mobile arsenite (As(iii)-bearing) anion and the comparatively less toxic and less mobile As(v)-bearing arsenate anion, and their interconversion, if any, is a critical issue in terms of the environment and health. In place of adsorption-based temporary removal, arresting these toxic species within stable crystalline cages of naturally occurring solids and minerals, made up of arsenic and other common elements, such as iron, has been considered as an important decontamination strategy in recent times. Evidently, designing such an environmental management plan requires information on the nucleation of such desirable phases and consequently warrants several in situ X-ray spectroscopic studies of arsenic and other common ions in the aqueous phase. While probing Fe-As aqueous solutions at certain pH ranges, the present work found a barely noted photo-oxidation phenomenon of As(iii) to As(v), which occurs under irradiation with high-flux synchrotron X-ray. Our X-ray absorption spectroscopy (XAS) experiments on the Fe and As K-edges, with the purpose of monitoring the in situ nucleation of Fe(iii)-As(iii) clusters and growth, as a function of pH, revealed this unforeseen photo-oxidation as the pH of the solutions was raised above 3. Our combined experimental and density functional theory-based studies proved that the accelerated photo-oxidation is primarily driven by reactive free radicals, notably the hydroxyl radical (OH center dot), generated through the radiolysis of water by the high-energy X-ray beam of very high brilliance, and this photo-oxidation consequently drives significant structural reorganization, in which Fe(iii)-As(iii)-containing tooeleite mineral-like clusters get converted into As(v)-adsorbed ferrihydrite-like moieties, which act as the driving force for arsenic oxidation.

We report here the results of a detailed magnetic, thermodynamic, and neutron powder diffraction (NPD) studies carried out on the double perovskite iridates Pr(2-x)SrxMgIrO6 (x = 0 and 0.5). Temperature dependent bulk DC susceptibility data clearly reveals a sharp antiferromagnetic (AFM) transition at 14.5 K in Pr2MgIrO6(x = 0). Next, a weaker signature of an AFM transition at a lower temperature (6 K) is observed in x = 0.5 i.e., Pr1.5Sr0.5MgIrO6 (PSMIO1505). The observed magnetic transitions are further corroborated by the presence of anomalies around the same temperatures in our T-dependent specific heat results. The charge states of both Pr and Ir cations have been confirmed to be the expected ones (3+ for Pr in both the compounds, while Ir is in a pure 4+ state for x = 0 and in a mixed 4+/5+ state for x = 0.5) from the core-level x-ray photoemission spectroscopy (XPS) measurements. Using neutron powder diffraction (NPD) the magnetic ground states and the magnetic moment values were determined for both compounds. Both the Pr- and Ir-sites undergo AFM ordering below the respective transition temperatures, designated by the propagation vector k = ( 1/2 , 0, 1/2 ), in both the compounds.

An exotic quantum mechanical ground state, i.e. the non-magnetic Jeff = 0 state, has been predicted for higher transition metal t2g4 systems, due to the influence of strong spin-orbit coupling (SOC) or in other words, due to unquenched orbital moment contribution. However, previous attempts to experimentally realize such a state in 5d4 systems had mostly been clouded by solid-state effects or the reduced strength of the renormalized SOC that might allow significant triplon condensation. Interestingly, a recent study on vacancy ordered double perovskite compound K2RuCl6 by Takahashi et al (2021 Phys. Rev. Lett. 127 227201) concluded that even within LS coupling regime the Ru4+ 4d4 ions, within isolated RuCl6 octahedra, strongly accommodate J multiplets having Jeff = 0 as the ground state with weakly interacting Jeff = 1 excitation, due to large unquenced Ru orbital angular momentum in the system. In the present report, we show results from the double perovskite La2ZnRuO6, where Ru4+ ions form isolated RuO6 octahedra but unlike K2RuCl6, they remain chemically connected via corner-sharing with nonmagnetic ZnO6 octahedra. Next, we move on to separate out the RuO6 octahedra further by doping the Ru-site with Ti4+, in order to probe the character of the Ru4+ ions within a different structural background. We find that the system stabilizes in P2 1/n space group with tilted octahedra without distortion as has been confirmed by the x-ray powder diffraction and x-ray absorption spectroscopic studies. Interestingly, the x-ray photoelectron spectroscopic valance band spectra indicated certain inhomogeneity around the half-doping region, while confirming insulating ground state for all. Moreover, unlike the vacancy ordered double perovskite cases, it is observed that here the Ru orbital angular momentum gets substantially quenched and only the Ru spin magnetic moments are realized.

In this study, we investigate the presence of the Griffiths-like anomaly in the geometrically frustrated antiferromagnet HoBaCo4O7+δ and globally its absence in ErBaCo4O7+δ, despite only small differences in the ionic radii, f-electron occupancy, and the corresponding crystal structures of the Ho3+ and Er3+-members. Previous studies have identified the Griffiths phase in the Dy-analog, DyBaCo4O7+δ, suggesting certain inherent features of this class of materials that regularly give rise to such anomalies. To explore the curious disappearance of such an anomalous feature in ErBaCo4O7+δ, we prepared a series of compounds with varying compositions Ho1−xErxBaCo4O7+δ (0≤x≤1) and systematically studied the evolution of various physical properties as a function of Er-doping. Our experimental studies, including X-ray diffraction (XRD), magnetic, X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), heat capacity, and muon spin relaxation spectroscopy (μSR spectroscopy), revealed that while the Griffiths-like anomaly indeed disappears with doping at the macroscopic level, signatures of inhomogeneity are retained in ErBaCo4O7+δ too, at least at the local level. Overall, our results highlight the significant role of ionic radius and local structural distortions in stabilizing the Griffiths phase in this class of systems.

We experimentally investigate the structural, magnetic, transport, and electronic properties of two d5 iridate double perovskite materials La2BIrO6 (B = Mg, Zn). Notably, despite similar crystallographic structure, the two compounds show distinctly different magnetic behaviors. The M = Mg compound shows an antiferromagnetic-like linear field-dependent isothermal magnetization below its transition temperature, whereas the M = Zn counterpart displays a clear hysteresis loop followed by a noticeable coercive field, indicative of ferromagnetic components arising from a non-collinear Ir spin arrangement. The local structure studies authenticate perceptible M/Ir antisite disorder in both systems, which complicates the magnetic exchange interaction scenario by introducing Ir-O-Ir superexchange pathways in addition to the nominal Ir-O-B-O-Ir super-superexchange interactions expected for an ideally ordered structure. While spin–orbit coupling (SOC) plays a crucial role in establishing insulating behavior for both these compounds, the rotational and tilting distortions of the IrO6 (and MO6) octahedral units further lift the ideal cubic symmetry. Finally, by measuring the Ir-L3 edge resonant inelastic X-ray scattering (RIXS) spectra for both the compounds, giving evidence of spin–orbit-derived low-energy inter-J-state (intra t2g) transitions (below ~1 eV), the charge transfer (O 2p → Ir 5d), and the crystal field (Ir t2g → eg) excitations, we put forward a qualitative argument for the interplay among effective SOC, non-cubic crystal field, and intersite hopping in these two compounds.

Strong spin–orbit coupling (SOC) in iridates has long been predicted to lead to exotic electronic and magnetic ground states. Ba2YIrO6 (BYIO) has attracted particular attention due to the expectation of a Jeff = 0 state for Ir5+ ions under the jj-coupling scheme. However, controversies surround the actual realization of this state, as finite magnetic moments are consistently observed experimentally. We present a multi-physics study of this system by progressively introducing nonmagnetic Sb5+ ions in place of Ir5+ (Ba2YIr​1−ySb​yO​6, BYISO). Despite similar charge and ionic radii, Sb​5+ doping appears highly inhomogeneous, coexisting with a fraction of nearly pure BYIO regions, as confirmed by X-ray diffraction (XRD). This aligns with observations in related compounds. While inhomogeneity creates uncertainty, the doped majority phases offer valuable insights. It is relevant that the inclusion of even small amounts of Sb​5+ (10–20%) leads to a rise in magnetization. This strengthens our previous suggestion that magnetic Ir ions form dynamic singlets in BYIO, resulting in a near-nonmagnetic background. The observed moment enhancement with nonmagnetic doping supports the breakdown of these singlets. Furthermore, the magnetization steadily increases with an increasing Sb​5+ content, contradicting the anticipated approach towards the Jeff = 0 state with increased SOC due to reduced hopping between Ir​5+ ions. This reinforces the presence of individual Ir​5+ moments. Overall, our findings suggest that Ba​2YIrO​6 might not possess sufficiently strong SOC to be solely described within the jj-coupling picture, paving the way for further investigation.

Spin-orbit coupling offers a large variety of novel and extraordinary magnetic and electronic properties in otherwise 'ordinary pool' of heavy ion oxides. Here we present a detailed study on an apparently isolated hexagonal 2H spin-chain d(4) iridate Sr3LiIrO6 with geometric frustration. Our structural studies reveal Li-Ir chemical order with desired stoichiometry in this compound, while x-ray absorption together with x-ray photoemission spectroscopic characterizations establish pure 5+ valence of Ir. We have established a magnetic ground state with finite Ir5+ magnetic moments in this compound, contrary to the anticipated nonmagnetic J(eff) = 0 state, through combined dc susceptibility, 7Li nuclear magnetic resonance (NMR), muon spin relaxation (mu SR) and ab-initio electronic structure studies. These investigations together with ac magnetic susceptibility and specific heat measurements reveal that despite having noticeable antiferromagnetic correlation among the Ir5+ local moments, this system does not magnetically order down to at least 0.05 K, possibly due to geometrical exchange frustration, arising from the comparable nearest- and next-nearest-neighbor interchain Ir-O-O-Ir superexchange interaction strengths with opposite signs. However, the zero-field mu SR analysis shows emergence of a considerable proportion of spin-freezing on top of a spin-fluctuating dynamic magnetic background down to the lowest measured temperature of 1.7 K, possibly due to some inhomogeneity and/or the much stronger intra-column Ir-Ir magnetic exchange interaction strength relative to the inter-column Ir-Ir ones. The linear temperature dependence of the magnetic specific heat (C-m) in both zero and applied magnetic fields, plus the power-law behavior of the NMR spin-lattice relaxation rate suggest a gapless spinon density of states in this charge gapped disordered magnetic ground state of Sr3LiIrO6.

Iron oxyhydroxide, a natural nanophase of iron found in the environment, plays a crucial role in regulating surface and groundwater composition. Recent research proposes that within the nonclassical prenucleation cluster growth model, subnanometer-sized clusters (olation clusters/Fe-13 delta-Keggin oxolation clusters) might act as the prenucleation clusters (PNCs) of ferrihydrite or iron oxyhydroxide solid phase. However, these clusters are difficult to characterize as they are only observable momentarily in low-pH, high-Fe concentration solutions before agglomerating into extended solids, keeping the controversy over the true nature of the PNCs alive. In this study, we introduce large quantities of zinc acetate salt (ZA) into iron chloride solutions at the olation-oxolation boundary (3.6 mM Fe3+ at pH similar to 2.6). Remarkably, this manipulation is found to alter the structural arrangement of these subnanometer clusters before blocking them in isolation for hours, even at pH 6, where extended iron oxyhydroxide phases typically precipitate. On the other hand, controlled addition of ZA allows partial unblocking, leading to anisotropic agglomeration into cylindrical rod-like structures. Experimental techniques such as synchrotron-based small-angle X-ray scattering, X-ray absorption spectroscopy, high-resolution transmission electron microscopy (TEM), and cryo-TEM, along with density functional theory (DFT) calculations, reveal the nature of the structural rearrangement and the crucial role of Zn2+ ions in cluster stabilization.

Here we explore the structural, magnetic and dielectric properties of Co based compound Na_5Co_15.5Te_6O_36 as a candidate of short-range magnetic correlations driven development of dielectric anomaly above Néel temperature of (T_N=) 50 K. Low temperature neutron powder diffraction (NPD) in zero applied magnetic field clearly indicates that the canted spin structure is responsible for the antiferromagnetic transition and partially occupied Co form short range magnetic correlation with other Co, which further facilitates the structural distortion and consequent development of dielectric anomaly above antiferromagnetic transition. Additionally, the temperature dependent magnetic heat capacity and electron spin resonance measurements reveal the presence of short-range magnetic correlations which coincides with an anomaly in the dielectric constant vs temperature curve. Moreover, significant changes in the lattice parameters are also observed around the same temperature, indicating presence of noticeable spin-lattice coupling. Further, sharp jump in the magnetic field dependent magnetization clearly indicates the presence of metamagnetic transition and magnetic field dependent NPD confirms that rotations of Co spins with applied magnetic field are responsible for this metamagnetic phase transition. As a result, this transition causes the magnetocaloric effect to be developed in the system, which is suitable for the application in low temperature refrigeration.

For arsenic decontamination from groundwater, arsenic crystallization is becoming adopted due to its sustainability and economic benefits. However, arsenic crystallization technology is a two-step process, which makes it complex and generates hazardous waste. Successful efforts toward making it a single-step process are presented here. The addition of nanorods and ball-milled zinc sulfide nanoparticles to arsenic-contaminated water result in highly monodispersed and high-arsenic-containing mineralized nanowaste with a crystalline structure similar to the mineral Tooeleite ((Fe3+6(As3+O3)4SO4(OH)4·4H2O)). This study reports the results of a short-term stability test based on a toxicity characteristic leaching procedure and a long-term stability test of the mineralized synthetic nanowaste produced from water treatment. The Tooeleite-like mineralized nanowaste passed short-term stability tests. Arsenic in the leachate were found to be 1.1 ± 0.2 mg L−1 and 4.8 ± 0.3 mg L−1 from waste generated by the nanorod and ball-milled nanoparticles, respectively. The crystallinity was well preserved, as observed from the post-stability-test diffraction patterns, consequently proving that the waste product can be non-hazardous and therefore would not require any secondary treatment before final disposal.

Four distinct classes of multiferroics are usually being discussed in the literature, in which ferroelectricity is respectively driven by electronic lone pairs, geometry, charge ordering, and magnetism. Each class has its own shortcomings for technological applications. Here, through a combined experimental and theoretical investigation, we propose a mechanism to achieve multiferroicity in a single phase by engineering the anionic network and creating local geometric distortions in fluorinated, vacancy-ordered brownmillerite Ca2Mn2O5-xFy. The system exhibits both ferroelectricity and an antiferromagnetic order above room temperature, pointing toward a novel route to multiferroicity by anion mixing.

The simultaneous presence of Fe3+ and As3+ ions in groundwater (higher ppb or lower ppm level concentrations at circumneutral pH) as well as in acid mine drainages (AMDs)/industrial wastewater (up to few thousand ppm concentration at strongly acidic pH) are quite common. Therefore, understanding the chemical interactions prevalent between Fe3+ and As3+ ions in aqueous medium leading to nucleation of ionic clusters/solids, followed by aggregation and growth, is of great environmental significance. In the present work, we attempt to probe the nucleation process of Fe3+-As3+ clusters in solutions of various concentrations and pHs (from AMD to groundwater-like) using a combination of experimental and theoretical techniques. Interestingly, our study reveals nucleation of primary FeAs clusters in nearly all of them independent of concentration or pH. Theoretical studies employed density functional theory (DFT) to predict the primary clusters as stable Fe4As4 units. The surprising resemblance of these clusters with known Fe3+-As3+ minerals at the local level was observed experimentally, which provides an important clue about solid-phase growth from a range of Fe3+-As3+ solutions. Our experimental findings are further supported by a stepwise reaction mechanism established from detailed DFT studies.

AbstractPreferred orientation in polycrystalline materials is one of the most challenging problems for structural analysis. Significant preferred orientation can severely affect the structure‐property analysis of the systems having substantial crystallographic anisotropy. Here, an extremely high degree of preferred orientation has been demonstrated in R‐block hollandite hexagonal PbFexV6−xO11 compounds, which has recently been shown to exhibit an unusual colossal electroresistance response that has a strong dependence on structural modifications. The present results warn against possible errors in understanding the evolution of the crystal structure of these hollandites, which might adversely affect the estimation of the influence of the same on their spectacular physical properties.

In the presence of strong atomic spin-orbit coupling (SOC), tending to the j - j coupling limit, 5d(4) iridates are speculated to possess a nonmagnetic J(eff) = 0 singlet ground state from atomic consideration, which invariably gets masked due to different solid-state effects (e.g., hopping). Here, we try to probe the trueness of the atomic SOC-based proposal in an apparently one-dimensional system, Sr3NaIrO6, with well-separated Ir5+ (5d(4)) ions. But all the detailed experimental as well as theoretical characterizations reveal that the ground state of Sr3NaIrO6 is not nonmagnetic. However, our combined dc susceptibility chi, Na-23 nuclear magnetic resonance (NMR), muon spin relaxation/rotation (mu SR), and heat capacity C-p measurements clearly refute any sign of spin freezing or ordered magnetism among the Ir5+ moments due to geometrical exchange frustration, while in-depth zero-field and longitudinal field mu SR investigations strongly point towards an inhomogeneous quantum spin liquid (QSL)-like ground state. In addition, the linear temperature dependence of both the NMR spin-lattice relaxation rate and the magnetic heat capacity at low temperatures suggest low-lying gapless spin excitations in the QSL phase of this material. Finally, we conclude that the effective SOC realized in d(4) iridates is unlikely to offer a ground state which will be consistent with a purely atomic j - j coupling description.

Non-Fermi liquid behavior in some fermionic systems has attracted significant interest in last few decades. Certain pyrochlore iridates with stronger spin-orbit coupling strength have recently been added to the list. Here, we provide evidence of such a non-Fermi liquid ground state in another mixed-valent metallic pyrochlore iridate Pb2Ir2O7-delta, through the combined investigation of electronic, magnetic, and thermodynamic properties as a function of temperature (T) and applied magnetic field (H). Resistivity measurement showed a linear temperature dependence down to 15 K below which it shows rho similar to T-3/2 dependence while magnetic susceptibility diverges as chi(T) similar to T-alpha (alpha < 1) below 10 K. While a strong negative Theta(CW) has been observed from Curie-Weiss fitting, the absence of any long-range order down to 80 mK only indicates the presence of strong inherent geometric frustration in the system. Heat capacity data showed C-p similar to T ln(T-0/T) beta T-3 dependence below 15 K down to 1.8 K. More importantly spin-orbit coupling strength by x-ray absorption spectroscopy was found to be weaker in Pb2Ir2O7-delta compared to other pyrochlore iridates. In the absence of any large moment rare earth magnetic ion, Pb2Ir2O7-delta presents a rare example of an iridate system showing non-Fermi liquid behavior due to disordered distribution of Ir4+ and Ir5+ having markedly different strengths of spin-orbit coupling which might offer a prescription for achieving new non-Fermi liquid systems.

In this paper, a comparative structural, dielectric, and magnetic study of two langasite compounds Ba3TeCo3P2O14 (absence of lone pair) and Pb3TeCo3P2O14 (Pb2+ 6s(2) lone pair) have been carried out to precisely explore the development of room temperature spontaneous polarization in the presence of a stereochemically active lone pair. In the case of Pb3TeCo3P2O14, mixing of both Pb 6s with Pb 6p and O 2p helps the lone pair to be stereochemically active. This stereochemically active lone pair brings a large structural distortion within the unit cell and creates a polar geometry, while the Ba3TeCo3P2O14 compound remains in a nonpolar structure due to the absence of any such effect. Consequently, polarization measurement under varying electric fields confirms room temperature ferroelectricity for Pb3TeCo3P2O14, which was not the case for Ba3TeCo3P2O14. A detailed study was carried out to understand the microscopic mechanism of ferroelectricity, which revealed the exciting underlying activity of a polar TeO6 octahedral unit as well as Pb-hexagon.

In this paper the structural, magnetic, and dielectric properties of langasite compound Pb$_3$TeMn$_3$P$_2$O$_{14}$ have been investigated as a candidate of short-range magnetic correlations driven development of dielectric anomaly above N$\acute{e}$el temperature of ($T_N$=) 7 K. Presence of dielectric anomaly, structural phase transition and a short range magnetic correlation at the same temperature (at around 100 K) as well as magnetic field dependent capacitance clearly indicate that this compound shows magnetodielectric coupling at around 100 K. In addition, unusual behaviour is observed in two polarization loop at room temperature and liquid nitrogen temperature, where coercive field at liquid nitrogen temperature is larger than room temperature. Further, $P$-$E$ loop at liquid nitrogen temperature with different frequencies also affirm that the coercive field and remnant polarization are firstly reduced (but very small value) but when frequency is further increased to 15 Hz and 100 Hz, both of them are enhanced. Therefore, a transition is observed at around 15 Hz in frequency dependent $P_r$ and $E_C$ curve, which may be usually attributed to the generalized pinning and depinning of the dislocation arrays to polarization.

Colossal electroresistance (CER) in manganites, i.e., a large change in electrical resistance under the influence of either an applied electric field or an applied electric current, has often been described as complimentary to the colossal magnetoresistance (CMR) effect. Mixed valent vanadates with active t2g and empty eg orbitals, unlike manganites, have not naturally been discussed in this context, as double exchange based CMR is not realizable in them. However, presence of coupled spin and orbital degrees of freedom, metal-insulator transition (MIT) accompanied by orbital order-disorder transition, etc., anyway make the vanadates an exciting group of materials. Here we probe a Fe-doped hollandite lead vanadate PbFe1.75V4.25O11 (PFVO), which exhibits a clear MIT as a function of temperature. Most importantly, a giant fall in the resistivity, indicative of a CER, as well as a systematic shift in the MIT towards higher temperature are observed as a function of applied electric current. Detailed structural, magnetic, thermodynamic and transport studies point towards a complex interplay between orbital order/disorder effect, MIT and double exchange in this system.

Spin-orbit coupling (SOC) offers a large variety of novel and extraordinary magnetic and electronic properties in otherwise `ordinary pool' of heavy ion oxides. Here we present a detailed study on an apparently isolated hexagonal 2H spin-chain d^4 iridate Sr_3LiIrO_6 (SLIO) with geometric frustration. Our structural studies clearly reveal perfect Li-Ir chemical order in this compound. Our combined experimental and ab-initio electronic structure investigations establish a magnetic ground state with finite Ir^5+ magnetic moments in this compound, contrary to the anticipated nonmagnetic J=0 state. Furthermore, the dc magnetic susceptibility (χ), heat capacity (C_p) and spin-polarized density functional theory (DFT) studies unravel that despite having noticeable antiferromagnetic correlation among the Ir^5+ local moments, this SLIO system evades any kind of magnetic ordering down to at least 2 K due to geometrical frustration, arising from the comparable interchain Ir-O-O-Ir superexchange interaction strengths, hence promoting SLIO as a potential quantum spin liquid candidate.